Steric-Effects-Directed B–H Bond Activation of <i>para</i>-Carboranes

Abstract

The controllable B–H bond activation of carboranes has long been a compelling challenge. However, as the symmetry of para -carborane places the same charge on all of its ten boron atoms, controlling the regiochemistry of B–H bond activation in these molecules has remained out of reach ever since their discovery. Herein, we describe how to use steric effects to achieve a regioselective process for B–H activation of para -carborane. In this strategy, B(2,8)–H or B(2,7)–H activation patterns were achieved by taking advantage of the π–π interactions between pyridine ligands. Interestingly, by employing host–guest interactions in metallacage compounds, B(2,8)–H bond activation could be avoided and exclusive B(2,9)–H bond activation can be achieved. Steric hindrance was also found to be beneficial for regioselective B(2,8)–H bond activation in metallacage species. In this work, we demonstrate that steric effects can be a promising driving force for controllable activation of the B–H bonds of carboranes and open new opportunities in this field.